In recent years, printing plates made of a photosensitive resin are rapidly coming into general use in various fields of printing because of their better handleability, higher productivity, lower price, and improved printing performance as compared with the conventional printing plates. There have been devised and put into practical use several processes for developing photosensitive resin plates by: (1) blowing off unexposed portions from the plates with compressed air or other means to form a relief; (2) spraying a developing solution under a constant pressure to the plates to form a relief; and (3) rubbing off unexposed portions from the plates with a brush or other means, while immersing the plates in a developing solution.
A developing solution for washing out the photosensitive resin plates in a developing process such as described in (3) above contains the dispersed resin from the unexposed portions washed off after the development. The developing solution has an increased resin content after washing out many photosensitive resin plates, causing various problems, e.g., the speed of development is decreased, and the dispersed resin is flocculated to form scum which is then adhered to the plates and the brush. Thus required are frequent disposal of the used developing solution and frequent preparation of a fresh developing solution.
To solve the above problems, some methods have been devised in which the used developing solution is recycled by removing resin components. For example, U.S. Pat. No. 5,124,736 discloses a method for filtering a developing solution in the developing unit and returning the filtrate to the developing unit for reuse as the developing solution. This method, however, is of a closed system, and the reuse of the waste developing solution as the developing solution requires once stopping the continuous development and allowing the pooled waste developing solution to stand for a long period of time (e.g., about 8 hours) so that the resin in the waste developing solution is flocculated and deposited. Thus the development and the waste disposal cannot be carried out in parallel. This method further has a defect that fine particles of resin components cannot be removed and the resin content of the developing solution is increase, lowering the speed of development.
In general, the used resin-containing developing solution has been treated for waste disposal as follows: The developing solution is transferred to another tank after the completing of development, and the resin and the developing agents contained in the developing solution, such as surfactants, are flocculated with a flocculant for making them harmless, after which the mixture is treated for separation of harmless liquids and solids by filtration or other techniques, followed separately by waste disposal. This method, however, requires suspending the developing operation for removing and treating the developing solution at the whole volume. In the case of developing machines requiring a developing solution in quantity and difficult to suspend the developing operation halfway, of which good representatives are automatic developing machines, the resin-containing developing solution is also to be treated in quantity, so that large size tanks, stirrers, and resins are need in a large scale for this treatment and it further takes a long time for suspension. Therefore, this method is not suitable for automatic developing machines.